The present invention relates to a method for forming a fiber-reinforced composite member, particularly to a method for forming fiber-reinforced composite members having various shapes by using reusable shape-retention auxiliary members.
Because fiber-reinforced composite materials composed of reinforcing fibers impregnated with thermosetting or thermoplastic resins are light in weight and have high strength, they are widely used for various structural parts of vehicles, vessels, aircraft, etc.
A fiber-reinforced composite member is usually formed from a plurality of prepregs each constituted by a fabric of reinforcing fibers impregnated with thermosetting or thermoplastic resins, and laminated on a forming plate of a predetermined shape to form a preform, which is then compressed into a fiber-reinforced composite member of a predetermined shape while heating. Though a pressuring bag film or bagging film is used at the time of heating of the preform under pressure, the preform is likely to be deformed due to fluidization of the resin in the preform during the forming process if the preform has a complex outer shape, resulting in unsatisfactory dimensional accuracy in the formed fiber-reinforced composite member. Accordingly, shape-retention means made of a silicone rubber, etc. have conventionally been placed adjacent to projections of the preform to prevent the deformation of the preform, thereby seeking to improve the dimensional accuracy of the formed fiber-reinforced composite member.
FIGS. 4 and 5 show an example of conventional methods for forming a fiber-reinforced composite member by using a shape-retention means. A preform 1 of a fiber-reinforced composite material disposed on a forming plate 4 is composed of a flat portion 11 and a plurality of rib portions 12, 12xe2x80x2. The shape-retention means 3 has a complementary shape to the preform 1, and has recesses 31, 31xe2x80x2 for receiving the rib portions 12, 12xe2x80x2 on a lower surface thereof. As is shown in FIG. 5, after fitting the shape-retention means 3 to the preform 1, the preform 1 and the shape-retention means 3 are completely covered by a bagging film 5. A sealant 6 provided on a periphery of the bagging film 5 adheres to the forming plate 4. After evacuating the inside of the bagging film 5 via an air-suction opening 7, the preform 1 and the shape-retention means 3 completely covered by the film 5 are heated under pressure to form a fiber-reinforced composite member.
It is necessary in the above conventional method to provide an integral shape-retention means 3 having a completely complementary shape to that of the preform 1. A lot of time and steps are required for forming such shape-retention means 3. Also, the shape-retention means 3 is made of a silicone rubber which shrinks during the formation process of the fiber-reinforced composite material because of forming pressure and a chemical reaction of the silicone rubber with the epoxy resin in the preform 1. As a result, as shown in FIG. 6, the recesses 31, 31xe2x80x2 of the once used shape-retention means 3 are out of alignment with the rib portions 12, 12xe2x80x2 of the preform 1, making it impossible to use the shape-retention means 3 repeatedly. Further, because an integral shape-retention means 3 should be formed in conformity with each preform 1 of a particular shape, a shape-retention means 3 for one preform 1 cannot be used for another preform 1.
Accordingly, an object of the present invention is to provide a method for efficiently forming a fiber-reinforced composite member by using a shape-retention means which is repeatedly reusable and adapted to preforms of different shapes.
As a result of intense research in view of the above object, the inventors have found that by using a shape-retention means composed of a proper combination of soft unit members deposed on the outer shape of a preform composed of a fiber-reinforced, the fiber-reinforced composite member can be formed easily at a low cost.
Thus, the method for forming a fiber-reinforced composite member according to the present invention comprises the steps of (a) placing a shape-retention means adjacent to at least one projection of a preform made of a fiber-reinforced composite material; (b) completely sealing the preform and the shape-retention means with a bagging film; and (c) forming the preform into a fiber-reinforced composite member by heating under pressure, the shape-retention means being composed of a plurality of soft unit members.
Though not restrictive, the shape-retention means is preferably composed of a plurality of units having simple cross-sectional shapes such as a triangular prism, a rectangular parallelepiped, a flat plate, etc., which may be obtained by dividing an integral shape-retention means covering an entire surface of the preform. More preferably, the units are in a shape having a cross section constituted by curves having no acute angles of 90xc2x0 or less. With simple shapes, the assembled shape-retention means provide a gradually changing contour, avoiding excess load from applying to a bagging film. However, the shape-retention means may partially have slight projections or recesses, thereby promoting ease of handling.
In a preferred embodiment of the present invention, the method for forming a fiber-reinforced composite member comprises the steps of (a) disposing a preform made of a fiber-reinforced composite material and having at least one projection on a forming plate; (b) placing a shape-retention means composed of a plurality of soft unit members adjacent to each projection of the preform; (c) completely covering the preform and the shape-retention means with a bagging film having a sealant attached to a periphery thereof; (d) adhering the sealant to the forming plate such that the preform and the shape-retention means are completely sealed by the bagging film; (e) evacuating the inside of the bagging film; and (f) heating the preform under pressure to form it into a fiber-reinforced composite member.